However, as his overall poll numbers plummet, it will be the loss of support from evangelical Christians - a cornerstone of Republican presidential campaigns - that will be of particular concern to the embattled Trump camp.

According to a Reuters/Ipsos opinion poll, Mr Trump had only a 1-point edge over Hillary Clinton among people who identified as evangelicals, down from a massive 12-point advantage for the Republican in July.

Christianity Today, a leading evangelical magazine, said in an editorial that Christians should not support a man whose life is based around “idolatry, greed, and sexual immorality”.

“The revelations of the past week of his vile and crude boasting about sexual conquest — indeed, sexual assault — might have been shocking, but they should have surprised no one,” wrote Andy Crouch, editorial director.

“Enthusiasm for a candidate like Trump gives our neighbors ample reason to doubt that we believe Jesus is Lord.

“They see that some of us are so self-interested, and so self-protective, that we will ally ourselves with someone who violates all that is sacred to us.”

“I previously called Donald Trump a ‘good candidate with flaws’ and a ‘flawed candidate’ but I now regret that I did not more strongly condemn his moral character. I cannot commend Trump’s moral character, and I strongly urge him to withdraw from the election.”

A member of Mr Trump's own evangelical advisory board, James MacDonald, said he was withdrawing his support unless the billionaire repented.

The megachurch pastor of Harvest Bible Chapel said Mr Trump's comments in the video were "truly the kind of misogynistic trash that reveals a man to be lecherous and worthless — not the guy who gets politely ignored, but the guy who gets a punch in the head from worthy men who hear him talk that way about women”.

However, some conservative Christians said they were standing by the Republican. James Dobson, of Family Talk radio, condemned Mr Trump's comments, but called Mrs Clinton's support for abortion rights "criminal".

"Mr Trump promises to support religious liberty and the dignity of the unborn. Mrs Clinton promises she will not," he said in a statement.

In a further blow, Glenn Beck, the right wing media personality, said opposing Mr Trump was the “moral, ethical choice” - and that he briefly considered voting for Mrs Clinton.

On Tuesday, Mr Trump stepped up his fierce attacks on his own party leaders, promising to teach Republicans who oppose him a lesson and fight for the presidency "the way I want to".